Instrumentation to determine the positive ion production rate in the ionosphere using the mass spectrometer



Jan. 17, 1967 3, JOHNSON I 3,299,266

INSTRUMENTATION TO DETERMINE THE POSITIVE IoN PRODUCTION RATE IN THE IONOSPHERE' USING THE MASS SPECTROMETER 2 Sheets-Sheet 2 Filed July 22, 1964 I I I i L5 5 5 1 g i 5 I POWER 20 ll SUPPLY \J I MASS SPECTRO- METER MASS SPECTROMETER ELECTRONICS SECONDARY EMISSION MULTiPLIER L 20 M M POWER ELECTROMETER v 7 Y7 SUPPLY DETECTOR l a TELEMETER CIRCUIT RECEIVER RECORDER INVENTOR CHARLES X JOHNSON United States Patent OfiiCt? 3,299,266 Patented Jan. 17, 1967 INSTRUMENTATION TO DETERMINE THE POSI- TIVE ION PRODUCTION RATE IN THE IONO- SPHERE USING THE MASS SPECTROMETER Charles Y. Johnson, Annandale, Va., assignor to the United States of America as represented by the Secretary of the Navy Filed July 22, 1964, Ser. No. 384,558 5 Claims. (Cl. 250-419) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention is directed to determining the positive ion production rate of ions in the ionosphere and more particularly to instrumentation for measuring the ion production rate.

Heretofore the method of deter-mining the ion production rate required measurement of the solar radiation at the top of the atmosphere and studying the attenuation of that radiation as it penetrates into the atmosphere. The cross section of the atmospheric constituents are measured, then, on the basis of the solar radiation, the absorption and ionization cross sections and a model atmosphere, the production rate of positive ions at any specific level within the atmosphere are mathematically calculated. Energetic secondary electrons produced in the photoionization process also produce positive ions and are allowed for in the calculation. The prior art method requires calculations and operations based on human effort which permits the possibility of many errors. Also, the method is slow, complicated, and has many variables which may result in errors.

Solar Radiation at Lyman cv()\=1216 A.) and all of the radiation below the O ionization threshold wavelength at h=1026 Angstroms is absorbed in the region of the upper atmosphere to produce the ionosphere. The photoionization process is dependent on the radiation wavelength and neutral constituents with which it interacts. The basic primary positive ion production is illustrated in FIG. 1 of the drawing and can be explained from the chemistry of the ionosphere as follows:

Above 100 kilometers molecular nitrogen N molecular oxygen 0 atomic oxygen 0 and atomic nitrogen N are the abundant neutral constituents of interest to ionospheric physics. (The trace constituent nitric oxide NO may be important in the production of the ionosphere below 90 km. and need not be considered here. It is ionized by the Lyman or radiation 0:12.16 A.).) Each constituent has an ionization threshold wavelength in angstroms as given in the following table and on the left side of FIG. 1.

The corresponding threshold ionization energy in electron volts is listed below the wavelength value. Thus when a solar ultraviolet photon whose wavelength is equal to or less than the value given impinges on the terrestrial atmosphere it may ionize the constituents to produce a positive ion and a free electron. For the less energetic radiation between 1026 A. and 910 A. it selectively ionizes 0 Radiation less than 796 A. ionizes all of the abundant atmospheric constituents present below -300 km., the altitude below which the sensible radio ionosphere exists. It the photon has a wavelength less than -37'0 A. it may upon collision with a neutral constituent eject the electron with sufiicient energy that the ejected electron may in turn collide with another constituent to ionize it by the process of electron impact according to the equation where M may be either an atom or molecule. Two processes, thence, are active in producing the positive ions and free electrons present in the ionosphere, direct photoionization and secondary ionization by energetic electrons ejected in the photoionization process. -Ionizing solar radiation is the initial energy source directly and indirectly for both processes. For brevity both processes are listed as photoionization in FIG. 1.

Once created the electrons remain free in the ionosphere, to be the refractive medium for radio waves, until they recombine with a positive ion. The positive ions follow a different path to their destruction with electrons. Consider for example 0+ created by photoionization or by a'charge exchange reaction with N 0+ does not readily recombine with an electron but is destroyed through ion-chemical reactions with N and O to produce NO+ and 0 These latter constituents readily combine with an electron in the process called molecular dissociative recombination in which the molecule is dissociated into its constituent atoms.

To understand in detail the processes which occur in the ionosphere one must know the primary production rates of the various ion species by photoionization processes, and the ion present in the ionosphere after ion chemistry has shuflied them. Dissociative recombination must then balance the production rate of the ionosphere when it is in an equilibrium state.

To date the production rates of the various ion species has not been directly measured, but has been implied from the absorption of ionizing solar radiation in the upper atmosphere as a function of altitude. The positive ion composition and the dissociative recombination rates of 0 and NO+ have been measured by ion mass spectrometer experiments flown on rockets.

The present invention provides a device and method by which both the primary and secondary positive ion production rate can be measured directly without any intermediate steps.

It is therefore an object of the present invention to directly measure the ion production rates of the various ion species in the ionosphere.

Another object is to make use of available equipment modified to directly measure the ion production rates in the ionosphere.

Still another object is to determine production rates of given species as a function of altitude.

Yet another object is to provide a method and apparatus for the mass spectral analysis of positive ions produced in the ionosphere at a given time.

Other objects of the invention will become apparent from the following specification taken in connection with the drawings wherein:

FIG. 1 illustrates the basic ion-electron production processes, ion-chemical reactions between positive ions and the neutral atmosphere and the ion-electron dissociative recombination processes which destroy the ionosphere;

FIG. 2 is a schematic representation of the device of the present invention and FIG. 3 represents the entrance screens for the different gases.

The device of the present invention makes use of any well known Mass Spectrometer adapted for ion composition analysis, for example, a device such as described in Patent Number 2,955,204 of Willard H. Bennett. A given volume of the upper atmosphere is electrically shielded from ambient ions and thermal electrons but open to the ambient atmosphere, ionizing solar radiation, and energetic secondary electrons ejected in the photoionization process. Ions produced within the volume 'by these means are measured by the mass spectrometer to give a rate of their formation within the specific volume.

Now referring to the drawings, there is shown by illustration, a schematic drawing of suitable instrumentation for carrying out the teaching of the present invention. As shown, the device makes use of a Radio Frequency Ion Mass Spectrometer 11 above which are assembled three grids 12, 13, and 14, such as wire mesh, of a high optical transmission type as well known in the art. As illustrated, the electrodes are cylindrical with enclosed ends away from the mass spectrometer to provide an electrically shielded volume or space confined by the electrodes and the end of the Radio Frequency Ion Mass Spectrometer. The mass spectrometer 11 is provided with the necessary electronic circuits 16, a secondary emission multiplier 17 is secured at the output of the mass spectrometer to amplify the output signals. The amplified output signals are directed to an electrometer detector 18 and then the signal is directed into a telemetering circuit 21 which telemeters the signal to a ground receiver 22 which receives and records the output signals according to the mass of the ions detected. A suitable power source 20 is provided for the electronics of the device as is well known in the art. In carrying out the teaching of the present invention the instrumentation is transported into the ionosphere on a suitable rocket which is not shown for simplicity of the drawings.

The electrodes 12, 13, and 14 secured to the mass spectrometer are provided with suitable potential differences to prevent ambient ions and electrons below a given threshold value from entering the volume. Electrode 12, the outermost electrode, is maintained at an appropriate negative potential with respect to the rocket vehicle to I repel undesired negative charged particles such as thermal negative ion and electrons of less than about 12 electron volts. Electrode 13 is held at ground potential and electrode 14 is maintained 'at a positive potential, preferably greater in absolute value than the negative potential on electrode 12. Electrode 14 prevents any positive charged particles such as positive ions from passing into the volume confined by the electrodes. Thus electrodes 12, 1'3, and 14 permit only the ambient atmosphere ionizing solar radiation and energetic electrons to enter into the volume formed by the electrodes. Obviously other electrode and operating conditions and configurations can perform the desired task.

In operation, the mass spectrometer, attached electrodes, and electrical accessories are assembled and prepared tor flight. The assembly of the outer electrodes, mass spectrometer and secondary emission multiplier need not be evacuated since it is to be used in the upper atmosphere which near vacuum; however, for cleanliness the assembly should be outgassed. For this purpose, the outer electrode assembly is covered by a suitable cover and sealed prior to outgassing and then evacuated, if desired. The seal can be broken after the device reaches a desired altitude 'and the cover removed by any well known method. The assembly is loaded onto a rocket vehicle and prepared for flight by connecting the electronics to a power supply. The power supply Will be turned on just prior to flight time, actuated by a pressure switch or by a command signal. Also the cover over the electrode end of the assembly may be removed just prior to firing or removed 'by any well known method after firing and reaching a certain altitude. The three electrode end of the assembly is provided with an opening to the ambient atmosphere which permits the ambient atmosphere to enter into the volume confined by the inner electrode 14. The electrodes 12 and 14, respectively, prevent undesired negative and positive particles from entering the volume due to the potential applied thereto.

Conventional fairings should be used to protect the de vice during powered flight through the sensible atmosphere.

When the instrument is open to the upper atmosphere there is a continual flow of ambient neutral gas constituents through the volume contained by electrode 14. Since the surrounding electrodes are transparent to the ionizing solar radiation and to the energetic secondary electrons in the ionosphere they enter the contained volume and produce positive ions of the different neutral species present. The ions produced are then analyzed and measured by the mass spectrometer and associated detection equipment. The abundance of each ion measured per unit time gives the production rate of that specie for the volume contained by 14. The mass spectrometer separates the ions according to their mass and accelerates them through the difierent stages to the secondary emis sion multiplier. When an ion passes through the analyzer it strikes the first dynode of the secondary emission multiplier tube producing secondary electrons, these secondary electrons then are multiplied as they strike successive dynodes. The output of the multiplier tube is directed to an electrometer detector and then to a telemetering system which telemeters an appropriate signal depending on the ions. The signal is received by a ground receiver which prints out a trace of the signals. From the received signals, the ionization rate can be determined. Collection and analysis of the produced ions will take place in about 10 seconds precluding any ion-chemical reactions shown in FIG. 1 from occurring. Thus, there is no requirement for complicated calculations or laboratory measurements to determine the production rate of positive ions in the ionosphere.

To differentiate between photoions and those produced by energetic secondary electrons which enter the measuring volume, the voltage on electrode 12 is swept to higher negative voltage thereby excluding high energy secondary electrons. Thus, it becomes possible to differenti'ate between primary photoionization and ionization by secondary energetic electrons.

The above description has been written envisioning a Bennett type mass spectrometer as the analyzer, however, any type, including magnetic types, can be used so long as the mass spectrometer is of the type in which the ions are formed outside of the mass spectrometer analyzer system.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Instrumentation for determining the positive ion production rate in the ionosphere which comprises:

an ion mass spectrometer for analyzing positive ions, means connected with said mass spectrometer for detecting ions analyzed by said mass spectrometer,

telemetering means connected with said detecting means for telemetering detected signals,

a ground receiver-recorder for receiving said telemetered signals and recording said signals which indicate the ion production rate, and

a positive ion and an electron electrical shield secured to the ion inlet end of said spectrometer to form a volume between said electrical shield and said mass spectrometer, said electrical shield admits ambient atmosphere, ionizing solar radiation and energetic secondary electrons to said volume whereby ion production occurs by the interaction of the solar radiation with the ambient atmosphere admitted to said volume formed by said electrical shield and said ions are analyzed by said mass spectrometer.

2. Instrumentation as claimed in claim 1 wherein said electrical shield comprises:

at least two electrodes spaced from each other to form said first electrode is at a negative potential, said volume. said second electrode is at ground potential, and 3. Instrumentation as claimed in claim 1 wherein said said third electrode is at a positive potential. electrical shield comprises:

first, second, and third coaxially disposed cylindrical 5 References cued by the Exammer Wire mesh electrodes equally spaced radially from Radiofrequency Mass Spectrometer for Upper Air Reeach other. search by J. W. Townsend, J r. from the Review of 4. Instrumentation as claimed in claim 3 wherein: Scientific Instruments, vol. 23, N0. 10, October 1952, pp.

said first, second, and third electrodes include wire 53854l.

mesh across their outer ends perpendicular to their 10 I I axis and equally spaced from each other. RALPH NILSON P I 1mm y Examine" 5. Instrumentation as claimed in claim 3 wherein: W. F. LINDQUIST, Assistant Examiner. 

1. INSTRUMENTATION FOR DETERMINING THE POSITIVE ION PRODUCTION RATE IN THE IONOSPHERE WHICH COMPRISES: AN ION MASS SPECTROMETER FOR ANALYZING POSITIVE IONS, MEANS CONNECTED WITH SAID MASS SPECTROMETER FOR DETECTING IONS ANALYZED BY SAID MASS SPECTROMETER, TELEMETERING MEANS CONNECTED WITH SAID DETECTING MEANS FOR TELEMETERING DETECTED SIGNALS, A GROUND RECEIVER-RECORDER FOR RECEIVING SAID TELEMETERED SIGNALS AND RECORDING SAID SIGNALS WHICH INDICATE THE ION PRODUCTION RATE, AND A POSITIVE ION AND AN ELECTRON ELECTRICAL SHIELD SECURED TO THE ION INLET END OF SAID SPECTROMETER TO FORM A VOLUME BETWEEN SAID ELECTRICAL SHIELD AND SAID MASS SPECTROMETER, SAID ELECTRICAL SHIELD ADMITS AMBIENT ATMOSPHERE, IONIZING SOLAR RADIATION AND ENERGETIC SECONDARY ELECTRONS TO SAID VOLUME WHEREBY ION PRO- 